In recent years, Ethernet (registered trademark) is built as a protocol lower than an internet protocol (IP) network for each sub-network connection between a corporate server and a client in order to build the IP network. In general, Ethernet is built by connecting a plurality of layer 2 or layer 3 switches each of which switches a packet on the basis of a media access control (MAC) address.
In Ethernet, a link aggregation technique is employed in which a plurality of links are treated as one virtual link so that the links have broadband features and redundancy. Specifically, since a channel capacity of a link aggregation is a sum of channel capacities of plural links, the broadband features may be obtained. Further, even if some of the plural links are broken, a switch automatically allots packets to other links for continuing communication, so that the redundancy may be achieved.
If a failure occurs on a link and quality of a packet is degraded, it is necessary to exactly identify on which link (referred to as a failure link) the failure occurs so as to maintain a network.
In order to identify a failure link, a network tomography technique is ordinarily employed. According to the network tomography technique, a monitoring apparatus connected to the network is provided to capture a packet which passes through the network. The monitoring apparatus captures a plurality of packets, and measures quality of each packet to diagnose quality degradation. The monitoring apparatus learns a link that a packet passes through by using a routing protocol. Then, the monitoring apparatus makes a table in which whether packet quality is degraded or not is mapped for each link that the packets pass through. The monitoring apparatus identifies a link such that each packet which passes through the link suffers from quality degradation as a failure link.
Japanese Laid-open Patent Publications No. 2009-543500 and No. 2006-238052 disclose related techniques